The unreliability of AF_UNIX datagram sockets

Corinna Vinschen
Thu May 20 19:25:59 GMT 2021

On May 20 09:46, Ken Brown wrote:
> On 4/29/2021 7:05 AM, Corinna Vinschen wrote:
> > I think it should be possible to switch to STREAM sockets to emulate
> > DGRAM semantics.  Our advantage is that this is all local.  For all
> > practical purposes there's no chance data gets really lost.  Windows has
> > an almost indefinite send buffer.
> > 
> > If you look at the STREAM as a kind of tunneling layer for getting DGRAM
> > messages over the (local) line, the DGRAM content could simply be
> > encapsulated in a tunnel packet or frame, basically the same way the
> > new, boring AF_UNIX code does it.  A DGRAM message encapsulated in a
> > STREAM message always has a header which at least contains the length of
> > the actual DGRAM message.  So when the peer reads from the socket, it
> > always only reads the header until it's complete.  Then it knows how
> > much payload is expected and then it reads until the payload has been
> > received.
> I think I'd like to go ahead and try to do this DGRAM emulation in the
> current (AF_LOCAL) code.  It shouldn't be too hard, and it would solve the
> unreliability problem while we look for a better way to handle AF_UNIX
> sockets.

Yeah, sounds like the way to go for now.


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